The invention relates to a photometric apparatus for single lens reflex cameras and of the type in which an exposure value is determined by photometry with a photoelectric transducer element which senses light reflected from an object being photographed which light is transmitted through a photometric optical system and is further reflected by at least one of the surfaces of a film and a shutter blind.
In a conventional single lens reflex camera, the light which is transmitted through a photographic optical system is made to be directly incident on a photoelectric transducer element which is interposed on a light path at a position nearer an object being photographed than a film. This arrangement requires the provision for storage of a photometric result until a shutter blind is allowed to operate. As a result, an expensive memory is required in a photometric system of this type. In addition, because photometry is interrupted when the film is being exposed, there resulted an inconvenience such that when the exposure factors vary, a close adherence to such variation can not be followed. Additionally, there is a need for a change-over switch which is operated upon shutter release in order to permit a recovery of the stored photometric value from the memory, thereby adding to the complexity and the possibility of occurrence in failures of the system.
There has been a proposal which overcomes such inconveniences by determining an exposure value by photometry with a photoelectric transducer element of light from an object being photographed which is transmitted through a photographic optical system and is reflected by at least one of the surfaces of a shutter blind and a film. However, as the light which is transmitted through the photographic optical system is weakened, the reflected light from the surface of either the shutter blind or the film will be still further reduced in intensity as a result of the diaphragm setting, presenting a difficulty in that the operation of the photoelectric transducer element becomes critical. The situation is even more aggravated by the fact that the circuit arrangement usually employed is such that the transducer element is applied with a voltage from an operational amplifier which receives an output therefrom. The voltage applied from the operational amplifier prevents a minimal output from the transducer element from being determined with a sufficient accuracy, thus making it impossible to provide photometry of light having a minimal intensity.